1. Field of the Invention
The present invention relates to a motor trouble detection device for use in an anti skid brake control system and particularly suitable for detection of locking state of a pump motor for circulating brake fluid.
2. Description of the Prior Art
As shown in FIG. 8, an anti skid brake control system (ABS) of a fluid circulation type includes an electronic control unit 51 which performs various computations and judgements based on the signals from wheel speed sensors S1, S2, S3, and S4 each respectively provided to wheels. The ABS further produces control signals for pressure control valves of its hydraulic system to control brake fluid pressure properly.
The electronic controller 51 is comprised of a wheel speed detector 52, a reference speed calculator 53, an anti skid controller 58, a solenoid driver 59, and a motor driver 60. The wheel speed detector 52 calculates actual wheel speed of each wheel based on the signals from each of sensors S1, S2, S3, and S4. The reference speed calculator 53 produces a reference speed signal based on the calculated actual wheel speeds.
The anti skid controller 58 judges that a wheel is locked when the reference speed signal is greater than the actual wheel speed(s) by a predetermined value, and gives a solenoid driver 59 a pressure reduction instruction to energize solenoids SOL1 and SOL2. A solenoid valve 62, which is normally opened, closes a brake fluid supply path extending from a fluid pressure source constructed by a master cylinder 61 and an accumulator 66. A solenoid valve 63, which is normally closed, closes a fluid discharge path. As a result, a brake fluid in a brake cylinder 64 flaws into a reservoir tank 65, and the brake fluid pressure in the brake cylinder 64 reduces.
As the brake fluid pressure reduction starts, the motor driver 60 makes a motor 30 to start so that a pump 31 sucks the brake fluid in the wheel cylinder 64 and returns the sucked brake fluid to the fluid supply side. However, when the wheel speed indicative of a locking symptom is improved by the fluid pressure reduction, the difference between the reference speed and the actual wheel speed(s) becomes smaller than the predetermined value. In this case, the anti skid controller 58 judges that the wheel(s) is released from the locked state, and gives the solenoid driver 59 a pressure increasing instruction to release the solenoids SOL1 and SOL2. As a result, the solenoid valves 62 and 63 return to the normal condition, as depicted in FIG. 8, and are ready for increasing the brake pressure.
According to the anti skid control brake system of a fluid circulation type, it is necessary to keep the pump driving motor being rotated while the brake fluid temporarily sucked from the wheel cylinder during the brake pressure reduction is forcibly returned to the master cylinder 64. However, if the motor does not rotate, it is impossible to perform the anti skid brake control properly. Therefore, a warning device is preferably provided for giving a warning to a vehicle driver when the motor is troubled.
An example of such a warning device was proposed in Japanese Patent Pulication (examined) No. H3-75377 issued Nov. 29, 1991, as shown in FIG. 9. A motor trouble detection circuit includes an anti skid control circuit 14 which calculates and produces a hydraulic pressure signal enabling that the wheels can obtain the maximum braking efficiency but does not go into a skid. The anti skid control circuit 14 produces and inputs a motor driving signal Se0 to one of input terminals of an OR-gate 28. A relay 18 is excited by the "turn-on" of a transistor Tr10 whose base is applied with the motor driving signal SeO through the OR-gate 28. The relay 18 has a contact point 18r through which an electric power from a battery 22 is supplied to the motor 30 for driving the pump 31, when the contact point 18r is closed. A fuse 20 is provided between the battery 22 and the contact point 18r. An operation switch 24 is provided for testing the warning device. A mono-stable multivibrator 26 is driven according to a voltage impressed thereto by operating the switch 24, and outputs a pulse signal Se1 for a predetermined period. This pulse signal Se1 is applied to the other input terminal of the OR-gate 28.
The warning device further includes a trouble detection and display means comprised of an exclusive OR-gate 32, a timer 34, a R-S flip-flop 36, a transistor Tr14, and a lamp 38, connected as shown in FIG. 9, is provided. The lamp 38 is lit up when other member of the warning device are turned on. The exclusive OR-gate 32 has two input terminals; one is connected to the output terminal of OR gate 28 and the other is connected to an electric power source +E through a resistance R0 whose value of resistance is well greater than the direct current resistance of the motor 30. The latter of input terminals of gate 32 is further connected to a contact point A provided therein to the motor 30 through a diode D0 for supplying a continuous current which is a pilot current.
Here, the operation of thus constructed warning device is described. First, when the operation switch 24 is off, the output from the mono-stable multivibrator 26 is low. Therefore, the output from the OR-gate 28 is also low. Furthermore, the pilot current is flowing to the motor 30 through the diode DO from the contacting point A. Therefore, the exclusive OR-gate 32 outputs a low level signal, As a result, each of members 36, Tr14, and 38 after the timer 34 does not operate.
However, when the motor 30 has a wire thereof broken, the pilot current is shut off so that the electrical potential at the contact point A is approximately the same as that of the electric source +E. Therefore, one of input terminals of exclusive OR-gate 32 becomes high, causing the exclusive OR-gate 32 to output a high level signal. A predetermined period after receiving this high level signal, the timer 34 outputs a high level signal causing the R-S flip flop 36 to be reset. The R-S flip flop 36 outputs a high level signal from an output terminal Q thereof, and the transistor Tr14 is turned on. As a result, the lamp 38 is lit so as to indicate that the motor 30 has a breaking of wire.
When the operation switch 24 is turned on, the OR gate 28 outputs a high level signal on receipt of the pulse signal Se1 from the mono-stable vibrator 26. Due to this high level signal, the relay 18 is excited to close the contact 18r. Since the motor 30 rotates if the motor 30 is normal and not troubled, it is possible to know that the motor 30 is in a normal condition by hearing the sound of the motor 30 which is rotating.
In this case, the high level signal from the OR-gate 28 is input to one of input terminals of the exclusive OR-gate 32. Furthermore, another high level signal is input to the other input terminal of the exclusive OR-gate 32 when the motor 30 rotates properly. Therefore, the exclusive OR-gate 32 outputs a low level signal, allowing the lamp 38 being not lit. However, just after the operation switch 24 is turned on, the terminal voltage of the motor 30 is zero due to an operational time lag of the contact 18r of relay 18. Accordingly, the voltage at the contact point A becomes low, and the warning lamp 38 is lit up to giving a warning of the motor trouble contrary to the fact. To prevent such an operational error of the warning lamp 38, the timer 34 is provided.
However, it is possible that the motor spindle is mechanically locked so that the motor spindle can not rotate, even if the motor 30 has no breakage of wire. In this case, since the potential at the input point A of the exclusive OR-gate 32 is high, the exclusive OR-gate 32 outputs a low level signal. Therefore, the warning lamp 38 is left as being not lit contrary to the fact that the motor spindle is locked and can not rotate. Thus, it is judged in error that the motor 30 is not troubled.
It is possible to detect the motor trouble even when the motor spindle is locked by monitoring the current on the side of motor driving circuit. However, a special circuit is necessary for the detection of this current, resulting in the increased cost of the device.